Preparation op pentacyclic lactones



niqotinic acid, tl iicyplre e carboxylic acids 2,857,385 PREPARATION F PENTACYCLIC LACTONES Martin Eric Kue hne, Summit, N, J., assiguor to Ciha Pharmaceutical Products, Inc., Summit, N. .L, a corporation of New Jersey No Drawing. Application April 17, 1956 Serial No. 578,595

2 Claims. (Cl. 260--286) This application relates to a new process for the preparation of reserpine and compounds similar thereto, their optical antipodes and the racemates thereof, as well as their salts.

More particularly the invention relates to a process for the preparation of compounds of the following formula;

wherein X represents the unsubstituted or substituted remainder of a benzene nucleus, Z stands for --GOOR or CH OH, R is hydrogen or lower alkyl, R stands for lower alkyl and R" represents hydrogen or an acyl radical. The substituents of the benzene nucleus may be for example halogen atoms, e. g. chlorine, bromine or fluorine; lower alkyl, e. g. methyl or ethyl; or preferably lower alkoxy, e, g. methoxy, ethoxy or methylenedioxy. These substituents are advantageously in and/or l'l-position of the reserpine ring skeleton, preferably in ll-position. R and; R, if alkyl radicals, are especially methyl or ethyl. An acyl radical is for example the radical .ofan aromatic, aliphatic, heterocyclicor araliphatic carboxylic or sulfonic acid, such as a lower fatty acid, e. gracetic acid or propionic acid; phenyl carboxylic acids such as alkoxyphenyl 'carboxylic acids, e. g. 4- methoxy benzoic acid, 3,4-dimethoxybenzoic acid, 3,4,5- trimethoxybenzoic acid, 3,4 methylenedioxybenzoic acid, 3,4-diethoxybenzoic acid, syringic acid or O-carbalkoxysyringic acids; alkox'yphenyl aliphatic carboxylic acids, e. g. alkoxy-cinnamic'acids such as dior trimethylcinnamic acid; monocyclicheterocyclic carboxylic acids, e. g. furane carboxylic acids such as furane-Z-carboxylic acid, pyridine ca boxylic acids such as 'nicotinic or isosuch as thiophene-Z-carbozrylic acid; or arylsulfonic acids such as benzenesulfonic acid or p,-toluenesul fonic acid.

These compounds may be laevo rotary, dextro-rotary or IQQQFDB Th eir rorrq aryx pounds, n racemates as well as the compounds of the; above-mentioned formula, wherein X, Z and R" havethe meaning given above and R represents a lower alkyl gro'up having at least two carbon atoms, or wherein Z, R and R have the meaning given below the first formulaand X represents the sub- 2,857,385 Patented Oct. 21, 1958 stituted remainder of a-benzene nucleus other than that in reserpine are described in my copending application Serial No. 576,833, filfed April 9, 1956, now abandoned. The compounds obtained according to the new process, laevo-rotary, dextrq rotary and racemic, in which R and R" are alkyl and acyl groups respectively, have valuable pharmacological activity. They show a hypotensive andsedative a'e'tivi-ty a'n'd'c'an be used as medicaments for the treatment of anxiety, nervousness, tension and filefital di s bfdfsf Bspe'cial1y valuab1e in this respect are the compounded the following formula:

' wherein Y stands for; hydrogen or m mor R and R stand for methyl or ethyl and R" represents the acetyl, 4 me noxybenzeyl, 3,4 dime thoxy'benzoyl, 3,4,5 tr'iiret-hoirybenzoyl, 3,4 rnethylenedioiiybehioyl, cinnafnoyl, 4'-niethoX-y einnafiioyl-, 3,4-dimethoxy cinnamoyl or 3,4,5- t'rirriethoxy-einnainoyl; furoyI-Z, nicotinoyl, or O carbetho'iry s ringeyl radical; The other compounds of the general rename indicated in the beginning are intermediates for the preparation of the phartiiacologically active compounds into which they can be converted according to known methods, which are exemplified on the laevorotary compounds in co ending application serial No. 526,780, filed August 5, 1955, by E. Schlittler ct alt, now Patent Number 2,824,874.

The new process of my' invention consists in converting a compound of the formula:

wherein X and R' have the meaning given above, or salts thereof intoa compound of theformula:

or salts thereof, t'reatnie'ntwith a dehydrating agent and, if desired, converting the lactone thus obtained into a compound of the general formula wherein X, Z, R and R have the aforesaid meanings, or salts thereof, by methods known per se.

Salts are more especially acid addition salts such as those with inorganic acids, for example, hydrohalic acids, e. g. hydrochloric acid; sulfuric acid, phosphoric acids, nitric acid or organic acids, for example, acetic acid.

Salts of free carboxylic acid compounds are preferably inorganic acids, for example, sulfuric acid, hydrohalic acids, e. g. hydrogen chloride, or organic acids, e. g. acetic acid, p-toluene sulfonic' acid, or borontrifluoride.

In the compounds obtained the hydrogen in the 3-position has the same stereospecific configuration as the lactone grouping. Thus, the over-all configuration of the nucleus is the same as in the epi-alloyohimbine series, e. g. as in reserpine. The splitting of the lactone grouping is performed with hydrolyzing or alcoholyzing agents such as alkali or earth alkaline metal hydroxides,

carbonates, lower alcoholates or amines.

In the compounds obtained, free carboxyl groups may be converted into lower carbalkoxy groups in the usual manner, for example, by treatment with lower diazoalkanes or lower alkanols in the presence of esterification catalysts. Esterified carboxyl groups may be hydrolyzed, for example, by treatment with alkaline agents, e. g. alkali metal hydroxides in lower alkanols. Free hydroxyl groups can be esterified in the usual way, preferably by reaction with acid halides, e. g. chlorides, or anhydrides. Amide groups can be converted into free or esterified carboxyl groups in the usual way. These subsequent reactions can be combined in any appropriate way and allowed to vary the final product of the process according to the formula given in the beginning.

The reaction may be carried out in the absence or presence of a solvent at room temperature or with heating in an open vessel or under pressure, preferably in an atmosphere of nitrogen.

The starting material can be used in the form of the optically active antipodes or the racemate. Racemates obtained in any stage of the process can be resolved to the optically active antipodes and may be used in either form for the remaining steps. racemates, may also be resolved. The usual method for resolving is used, e. g. the reaction of the racemate with an optically active base or acid, as the case may be, and separating the diastereoisomeric compounds by frac- Final compounds, if.

tional crystallization, and setting free the desired optically active compound.

The starting materials used in the process of the inventlon are known or can be made by known methods.

They can be obtained, for example, by total synthesis in the following manner: quinone is reacted with 1,4- butadiene-l-carboxylic acid in a Diels-Alder addition. The 6,9-dioxo-1,4,5a,6,9,10a-hexahydronaphthalene 1,8- carboxylic acid of the formula:

is then reduced with sodium borohydride to tie-hydroxy- 9 oxo 1,4,5a,6,9,10 hexahydronaphthalene l5 carboxylic acid yielding by oxidation with perbenzoic acid, 2,31: oxido 6B hydroxy 9 oxo 1,2,3,4,5a,6,9,10aoctahydronaphthalene-lfl-carboxylic acid of the formula:

This compound, after esterification with diazomethane is subjected to a Meerwein-Ponndorf reduction with aluminum isopropoxide to yield the (1 8+ 9fi)-lactone of 3,66 oxido 9e hydroxy 3,4,5a,6,9,10a hexahydronaphthalene 1;3 carboxylic acid of the formula:

which by addition of a lower alkanol to the double bond in l-position is converted into a (1fi 9fi)-lactone of 2alower alkoxy-3,6;3-oxido-9 3-hydroxy 1,2,3,4,5a,6,9,l0aoctahydronaphthalene-lfl-carboxylic acid. Addition of bromohydrine to the double bond in 7-position results in the (lfl 9fi)-lactone of Za-IOWer alkoxy-3,6fi-oxido-7abroino-SB, 9fl-dihydroxy-l,2,3,4,5a,6,7,8,9,IOa-decahydmnaphthalene-1 fl-carboxylic acid. Oxidation with chromic acid to the corresponding 8-oxocompound, followed by reduction with zinc and acetic acid yields Za-lOWl' alkoxy' 3,3 hydroxy 8 oxo l,2,3,4,5a,8,9,10a-0Ctahydronaphthalene-lfl-carboxylic acid of the formula:

Esterification with diazomethane, acetylation with acetic acid anhydride in pyridine, oxidation with osmium tetroxide and oxidative degradation with periodic acid gives 2a-lower alkoxy 3B-acetoxy-5fi-aldehydo-6,3-carboxy methyl-cyclohexane-lfi-carboxylic acid methyl ester. This after esterification with diazomethane is condensed with a tryptamine of the formula:

assesses "wherein. X has the aforesaid .meahing to yield a compound of the formulaz Reduction with sodium borohydride and ring closure with heating results in a compound of the formula:

H OCO-CH:

on H

By treatment of the latter with phosphorus oxychloride, ring closure occurs to form compounds of the formula:

H CHsOOCT O'R H wherein A represents an anion, e. g. a chloride ion, which compounds can be reduced by treatment with hydrogen in statu nascendi, e. g. by treatment with sodium borohydride to compounds of the general formula:

which may be converted into the desired starting material by methods known per se, for example, by hydrolysis in alkaline medium.

According to the conditions used in the reaction the products may be obtained free or in the form of their salts. Thus, bases obtained are converted into the salts the M. P. 267269 in the customary manner, and thefree bases can. be

obtained as usual from the salts. As salts especially acid addition salts are contemplated, e,,g. those of the hydrohalic acids, e. g. hydrochloric acid; nitric acid, sulfuric acid, phosphoric acids, perchloric acid; acetic, citric, oxalic, tartaric, ascorbic, methane sulfonic, hydroxyethane sulfonic, p-toluene sulfonic acid or salicylic, p-amino-salicylic acid or acetyl-salicylic. Free carboxylic acid compounds can be in the form of their metal salts, e. g. alkali or alkaline earth metal salts.

The invention comprises also any process, wherein an intermediate obtainable at any stage of the process is used as starting material and the remaining steps are carried out. I I

The example which follows isgiven in the way of illustration and shall not be construed as a limitation. Many modifications will appear obvious to the man skilled in the art and it is intended that such obvious modifications are also comprised by my invention. Temperatures are given in degrees centigrade.

Example 0.5 g. of 3-isoreserpic acid hydrochloride is heated during 50 minutes in 25 ml. of acetic anhydride containing two drops of acetic acid in an atmosphere of nitrogen. The acetic anhydride and acetic acid is removed under reduced pressure and the residual material taken up in ml. of water containing 3 ml. of hydrochloric acid. After extractions with 20 ml. portions of chloroform, the aqueous solution is made basic (pH 8) with aqueous ammonia. Extraction with 6 portions of 20 ml. each of chloroform and evaporation of the chloroform under reduced pressure yields reserpic acid lactone, M. P. 310-315". The product is identified by mixed melting point and infrared spectrum as being identical with reserpic acid lactone obtained from reserpine.

The 3-iso-reserpic acid hydrochloride used as starting material in the above example is obtained as follows:

'1 g. of methyl 3-iso-reserpate is refluxed for three and one-half hours in 60 ml. of methanol containing 4g. of potassium hydroxide in an atmosphere of nitrogen. The methanol is removed under reduced pressure, 50 ml. of water are added and the solution is extracted four times with 20 ml. portions of chloroform. The water is removed under reduced pressure, the residual potassium hydroxide and potassium salt of 3-iso-reserpic acid is taken up in 60 m1. of methanol and acidified to pHZ with 7 N hydrochloric acid. Potassium chloride is removed by filtration, the residue washed with 100 ml. of a mixture (4:1) of chloroform:methanol. The combined organic solutions are evaporated to dryness under reduced pressure. By addition of 30 m1. of a mixture (4:33) of chloroformzmethanol and by chilling in ice the crystallized hydrochloride of 3-iso-reserpic acid of (with decomposition) is obtained which is isolated by filtration.

What is claimed is:

1. Process for the preparation of a member of the group consisting of a compound of the formula:

n no n ing a member of the group consisting of a compound of the formula:

in which Y and R have the above-given meaning, and

an acid addition salt thereof, with a dehydrating agent selected from the group consisting of phosphorus pent- '8 oxide, acetic anhydride, phosphorus oxychloride and thionyl chloride, in the presence of a Lewis acid.

2. Process according to claim 1, wherein acetic acid anhydride is used in the presence of acetic acid.

References Cited in the file of this patent pages 303- 

1. PROCESS FOR THE PREPARATION OF A MEMBER OF THE GROUP CONSISTING OF A COMPOUND OF THE FORMULA: 